NORTH AMERICAN LATER TERTIAIJV AND QUATERXARY BRYOZOA. 



125 



MICROPORELLA HEERMANNI Uabb and Horn, 1862. 



Plate 37, figs. 1, 2. 



1862. Reptescharellina heermanni Gabb and Horn, Monograph of fossil Polyzoa of the Secondary 

 and Tertiary formations of North America, Journal Academy Natural Sciences of Phila- 

 delphia, ser. 2, vol. 5, p. 147, pi. 20, fig. 30. 



Description. — The zoarium incrusts shells. The zooecia are large, elliptical, 

 swollen, separated by a furrow, convex; the frontal is formed by a granular tremo- 

 cyst perforated by numerous small pores. The apertura is semilunar, transverse; 

 the peristome is thin, somewhat salient, deprived of spines resistant to fossilization. 



I 



Fig. 21. — Subgenus Diporula Hincks, 1879. 



A-F. Diporula verrucosa Peach, 1868. A. Zoarium, natural size. B. Zooecia with avicularia and 

 mandibles, X 25. (A, B, after Hincks, 1880.) C, D. Growing extremity of a zoarium. Theendsofthe 

 last formed row of zooecia have a double slope, like the roof of a house with a raised, rounded, slightly 

 overlapping ridge at the top. On each side of this are usually five tubular holes and one or two lower 

 down on the side. At the bottom of these tubes is a membrane which has one, two, or even more minute 

 perforations. D shows the ridge of the roof and rosette pores, X 85. E. Operculum, X 85. (C-E, after 

 Waters, 1878.) F. Mandible, X 85. (After Waters, 1885.) 



G-I. Diporula hastigera Busk, 1884. G. Operculimi, X 85. H. Mandible, X 85. (After Waters, 

 1889.) I. Section of zooecium showing anatomical structure. (After Jullien, 1903.) ar, aviculariimi; 

 c, corniculum; ca, calcite; co, compensatrix;/, fenestrule (=ascopore);/r, frontal; gt, tentacular sheath; 

 i, irisoid; mo, opercular muscles; of, inferior orifice of the corniculum; op, operculum; t, tentacles; r, 

 dorsal. The corniculum is not a tube allowing communication of the ascopore with the tentacular 

 sheath as Jullien thought, but it is a simple fold of the compensatrix probably determined by the size 

 of the tentacles. 



